<p>To achieving successfully commercial nuclear fusion energy, fully understanding of the interaction between plasma particles and plasma facing components is one of the essential issues. Tungsten, due to good thermal and mechanical properties such as high thermal conductivity and melting temperature, is one of the most promising candidates. However, the plasma facing components interacting with the extreme environmental conditions such as high temperature and radiation may lead to nanostructure formation, sputtering and erosion that will lead to material degradation. And these deformations may influence not only properties of plasma facing components but also might affect the plasma itself. For example, the contamination of plasma with a few amounts of tungsten, a high Z element, as a result of erosion or sputtering may cause core plasma cooling that results in loss of plasma confinement. Additionally, the retention of hydrogen isotopes, especially tritium, in tungsten is essential issue because of its radioactivity and market value.</p> In this study, deuterium trapping in tungsten is analyzed by molecular dynamics method and the effect of pre-irradiation on trapping is studied. Non-cumulative studies show that the increase in the energy of hydrogen isotopes rises the absorption rate, the initial implantation depth, and the average resting time for initial implantation. Additionally, the effect of implanted deuterium due to pre-irradiation on the hydrogen isotopes trapping is analyzed by combining both cumulative and non-cumulative simulations, and results indicate that while the increase in the pre-irradiation time raises the absorption rate of deuterium with higher energy than 80 eV, it causes a decrease the initial implantation depth and the average resting time for initial implantation because of deuterium-deuterium interactions. Additionally, the deuterium-deuterium interactions may transfer enough energy to implanted deuterium to start a motion which may lead to deeper implantation or escaping from the surface of tungsten. The escaping from surface as a result of deuterium-deuterium interaction could explain the decrease in accumulation rate of deuterium while absorption rate rises.